Breath masks also safeguarded the wearer from minor differences in atmospheric pressure. Typical air canisters provided one hour of breathable atmosphere before replacement of the canister was required. The typical breath mask weighed roughly 1.5 kilograms. These masks offered no protection from extreme temperatures or a hard vacuum. In some cases, respirators were built into a person as cybernetics, if they suffered severe enough injuries that they cannot live otherwise. Notable examples include Darth Plagueis as well as Darth Vader and General Grievous.